Transmit power efficiently
Step-up transformers raise potential difference for transmission; step-down transformers reduce it for consumers. Use the turns ratio and explain why high voltage reduces current and cable heating for a given power.
GCSE Physics resources
AQA GCSE Magnetism and electromagnetism
Transformers and the National Grid
Step-up transformers raise potential difference for transmission; step-down transformers reduce it for consumers. Use the turns ratio and explain why high voltage reduces current and cable heating for a given power.
Start here
The quick revision snapshot
Step-up transformers raise potential difference for transmission; step-down transformers reduce it for consumers. Use the turns ratio and explain why high voltage reduces current and cable heating for a given power.
By the end, you should be able to…
- Explain transmit power efficiently using precise physics language.
- Apply the relevant equations, diagrams or practical method to an exam-style situation.
- Use the mini quizzes and practice answers to identify and correct a misconception.
Core learning content
Learn the idea before you practise it
Start with this short teaching sequence for Transformers and the National Grid. Read the model, use the visual, then test your recall before moving into examples and exam practice.
Build the picture
A transformer works with alternating current because the changing current in the primary coil creates a changing magnetic field. The turns ratio sets the voltage ratio. For a fixed transmitted power, higher voltage means lower current, so less energy is wasted heating the cables.
Use the right relationship
Choose a relationship because of the physical change in the question, not because it is familiar. Transformer ratio: Vₚ ÷ Vₛ = Nₚ ÷ Nₛ (V, turns). Power in an ideal transformer: VₚIₚ = VₛIₛ (W, V, A). Magnetic field strength idea: closer field lines = stronger field (qualitative). Keep the unit next to each value while you substitute.
What a strong answer does
Identify primary/secondary, choose the ratio equation, calculate the missing value and finish with the transmission explanation. Before writing, underline the command word and identify the information that matters. Keep a calculation as equation, substitution and answer with unit; keep an explanation as a linked chain using because, so or therefore. Finish by checking that the final sentence answers the exact context in the question and that the number, direction or conclusion agrees with the evidence given.
Retrieval practice
Quick checks
Answer without looking back first. The feedback explains the model, so a wrong answer still helps you learn.
Mini quiz 1
Check the core idea
Mini quiz 2
Apply the model
Mini quiz 3
Use exam precision
Try it
Transformer turns-ratio model
How does a turns ratio change the secondary potential difference?
What to notice: the readout and written explanation remain available if you do not use the controls.
Worked examples
See the method being built
Cover the answer, attempt the method and then compare your physics language as well as the number.
Example 1 · Turns ratio
Primary: 200 turns, 230 V. Secondary: 1000 turns. Find secondary p.d.
- Use Vs/Vp = Ns/Np.
- Ratio = 1000/200 = 5.
- Multiply 230 by 5.
Show the answer
Vs = 1150 V.
Example 2 · Grid loss
Explain why the Grid transmits at high voltage.
- Use P = VI.
- For fixed power, high V means low I.
- Link low I to less heating loss.
Show the answer
Lower current reduces energy transferred to thermal stores of cables due to resistance.
Example 3 · AC requirement
Explain why a transformer does not work on steady d.c.
- Transformer needs changing magnetic field.
- Steady d.c. makes constant field.
- No induced secondary p.d.
Show the answer
A steady current does not continually change the magnetic field, so no continuous p.d. is induced in the secondary coil.
Misconception clinic
Common wrong turns
Each of these is tempting because it sounds almost right. Replace it with the precise physics before you meet it in a question.
- Using d.c. as transformer input.
- Reversing primary/secondary ratio.
- Saying high voltage itself “uses less energy” without mentioning current/heating.
Independent practice
Exam-style questions
Use the working space first. Reveal the guidance only after you have committed to an answer, then improve the exact part that would gain the next mark.
1. State why transformers need alternating current.
[1 mark]Show answer and marking guidance
AC produces a changing magnetic field.
2. A transformer has twice as many secondary turns as primary turns. State voltage change.
[2 marks]Show answer and marking guidance
Secondary voltage is twice primary voltage for an ideal transformer.
3. State what a step-up transformer does.
[1 mark]Show answer and marking guidance
Increases potential difference.
4. Explain why step-down transformers are used before homes.
[3 marks]Show answer and marking guidance
They reduce high transmission voltage to a safer/useful supply voltage.
5. State why high current in Grid cables is undesirable.
[1 mark]Show answer and marking guidance
It causes more heating losses due to resistance.
6. State whether this route is Combined Science content.
[1 mark]Show answer and marking guidance
No; it is AQA GCSE Physics Higher Tier content.
Questions pupils ask
GCSE Physics FAQs
What is the key idea in Transformers and the National Grid?
Use field-line direction and the right-hand rule carefully. Electricity and magnetism are linked: current creates a magnetic field, and changing magnetic fields can induce a potential difference.
How should I practise Transformers and the National Grid?
Read the snapshot, attempt the worked examples without looking, complete the mini quizzes and then use the practice questions to check your wording and method.
Next step
Keep your revision moving
Physics sticks when you move between explanation, retrieval and application.